Test: Plant Kingdom b- Gymnosperms & Angiosperms (April 12) - NEET MCQ

Gymnosperms

• Gymnosperms are not the first terrestrial plants to possess vascular tissues.
• They are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes.

Pteridophytes

• Pteridophytes are the first terrestrial plants to possess vascular tissues.
• They are a phylum of plants, also known as ferns and fern allies.
• These plants reproduce and disperse via spores, which makes water a necessary element for their fertilization process.
• They are vascular plants (they have xylem and phloem) that reproduce via spores, and their life cycle involves alternation of generations.

Therefore, the mismatched pair is option B. The first terrestrial plants to possess vascular tissues were Pteridophytes, not Gymnosperms.

Formation of Functional Megaspore

• In angiosperms or flowering plants, megaspores are produced by the process of meiosis in the ovule, a structure within the ovary of the flower. Specifically, a specialized cell in the ovule, called the megasporocyte or megaspore mother cell, undergoes meiosis to produce four megaspores.

The Functional Megaspore

• Out of the four megaspores, typically only one megaspore becomes functional and the other three degenerate. This functional megaspore is the cell that will continue to develop into the female gametophyte.

Development into the Embryo Sac

• The functional megaspore then undergoes three rounds of mitosis to form eight nuclei within a single cell. This cell becomes the embryo sac, which is the mature female gametophyte in angiosperms. The embryo sac is crucial in plant reproduction as it houses the egg cell that is fertilized to form a new plant.

Fig: This figure depicts how functional megaspore develops into embryo sac.

One male gamete fuses with the egg (n) to form a zygote and the other male gamete fuses with the secondary nucleus (2n) to form the primary endosperm nucleus.

Let's understand it:

Double fertilization is a unique process in angiosperms (flowering plants) where two sperm nuclei from the male pollen grain fertilize two cells in the female ovule. This process results in the formation of a diploid (2n) zygote and a triploid (3n) primary endosperm nucleus.
Fertilization of the Egg Cell

• In the first fertilization event, one male gamete (sperm cell) fuses with the egg cell in the embryo sac.
• The egg cell is a haploid cell (n), meaning it contains a single set of chromosomes.
• When the haploid male gamete fuses with the haploid egg cell, they form a diploid zygote (2n), which contains two sets of chromosomes one from each parent.
• The zygote then develops into an embryo, which will eventually become a new plant.

Fertilization of the Secondary Nucleus

• The second fertilization event involves the fusion of the second male gamete with the secondary nucleus or central cell of the embryo sac.
• The secondary nucleus is a diploid cell (2n), containing two sets of chromosomes.
• When the haploid male gamete fuses with the diploid secondary nucleus, they form a triploid (3n) primary endosperm nucleus.
• This primary endosperm nucleus develops into the endosperm, a tissue that provides nourishment to the developing embryo.

The division of angiosperms into monocotyledons (monocots) and dicotyledons (dicots) is a crucial aspect in the study of botany. This categorization is primarily based on the structure and characteristics of the plant's seed.

Significance of the Division

• The division into monocots and dicots provides vital information about the plant's seed structure, which can help in identifying the plant species.
• This categorization also provides insights into other plant characteristics, such as the arrangement of vascular bundles, the structure of the flower, and the pattern of leaf venation.
• Understanding whether a plant is a monocot or dicot can also be useful in predicting its growth pattern and its response to environmental factors.

A - Sporophytic generation (2n)

B - Gametophytic generation (n)

The life cycle of plants is categorized into two distinct phases: the haploid gametophyte phase and the diploid sporophyte phase. These phases alternate in what is known as the alternation of generations. The dominance of one phase over the other varies among different plant groups.

Pteridophytes

• In pteridophytes, which include ferns and their allies, the sporophyte phase is dominant. This means that the plant we typically recognize as a fern is the sporophyte stage.
• The gametophyte stage in pteridophytes is relatively short-lived and is often an inconspicuous, small, green, heart-shaped structure.

Gymnosperms

• The gymnosperms, such as pines and spruces, also have a dominant sporophyte phase. The large, familiar trees we recognize are the sporophytes.
• The gametophyte stage in gymnosperms is reduced and dependent on the sporophyte for nutrition. It is confined within the cones and seeds.

Angiosperms

• Like gymnosperms, angiosperms (flowering plants) also have a dominant sporophyte phase. The plants we recognize as flowering plants are sporophytes.
• In flowering plants, the gametophyte stage is extremely reduced and is entirely dependent on the sporophyte for sustenance. It is confined within the flowers and seeds.

(A) Pteris - Pteridophyte
(B) Cedrus - Gymnosperm
(C) Sonchus - Angiosperm
(D) Marchantia - Bryophyte

• Pteris is a genus of ferns and belongs to the group Pteridophytes.
• Cedrus commonly known as Cedar, is a genus of coniferous trees in the plant family Pinaceae and belongs to the Gymnosperms group.
• Sonchus also known as Sow thistles, is a genus of flowering plants in the dandelion tribe within the sunflower family and belongs to the Angiosperms group.
• Marchantia is a genus of liverworts and belongs to the Bryophyte group.

So, the correct answer is A: A-(ii), B-(iii), C-(iv), D-(i).

Smallest angiosperm is Wolffia microscopici, while Raffesla amoldii is the parasitic plant with world's largest flower.

Zoomed in portions of leaves show parallel venation in plant A, a characteristic of Monocotyledonae except for a few and reticulate venation in plant B, a characteristic of dicotyledonae.

Angiosperms, also known as flowering plants, are the most diverse group of land plants. They are classified into two main classes: Monocots and Dicots.

(i) Monocots (Monocotyledonous Plants)

• Monocots are a type of angiosperm that contains only one cotyledon, or embryonic leaf, in its seed.
• Common examples of monocots include grasses, lilies, orchids, and palms.

(ii) Dicots (Dicotyledonous Plants)

• Dicots are a type of angiosperm that contains two cotyledons, or embryonic leaves, in its seed.
• Common examples of dicots include roses, sunflowers, and maples.